The subject of the present invention is a device for respiratory assistance which can be used on patients in whom spontaneous respiration is absent or inadequate, whether or not said patients are placed under artificial respiration.
Various devices are known, such as masks and oral, nasal, endotracheal and tracheotomy probes or cannulas, which are intended to form the junction between an artificial respiration and/or anesthesia apparatus and the respiratory tract of a patient. These devices, essentially in the form of tubes, can, depending on the circumstances, include immobilizing means such as flanges or collars in the vicinity of the proximal end for holding them on the mouth or nose of the patient, or inflatable balloons in the vicinity of the distal end for holding them by friction in the trachea.
The known devices have important disadvantages. Thus, for example, when a tube of a known type is disconnected from the artificial respirator and the patient needs oxygen-enriched air, it is necessary to introduce into said tube a probe which is connected to an oxygen source. Moreover, in cases of inadequate spontaneous respiration, the patient must necessarily remain connected to the respirator until spontaneous respiration has been completely re-established.
To overcome these disadvantages, it has already been proposed, for example in documents EP-A-0 390 684 and EP-A-0 701 834, to provide devices for respiratory assistance which, in addition to the main channel formed by the tube, comprise at least one auxiliary channel, for example formed in the wall of said tube, permitting injection of a jet of respirable gas (oxygen, air or air/oxygen mixture) intended to ventilate the patient, this auxiliary channel opening into the main channel in the vicinity of the distal end of the latter.
Of course, these latter known devices for respiratory assistance include safety means which are able to stop the functioning of the device in the event of overpressure in the respiratory tract of the patient and/or in said tube.
The object of the present invention is to improve said devices for respiratory assistance in order to increase the safety of their use still further.
To this end, according to the invention, the device for respiratory assistance comprising a tube which forms a main channel and which is intended to be connected via its distal end to the respiratory tract of a patient so that said main channel connects the respiratory system of said patient to the outside, said device moreover comprising at least one auxiliary channel connected to a source of respirable gas so as to permit the insufflation of a jet of such a respirable gas into said respiratory system, and opening into said main channel in the vicinity of the distal end of the latter, is distinguished by the fact that, in the conduit connecting said source of respirable gas to said auxiliary channel, it includes:
toward said source, a device for loss of head which is able to limit the flow rate and the pressure of said respirable gas available at the outlet of said source, and to impose on said jet of respirable gas a predetermined flow rate value and a predetermined pressure value; and
toward said auxiliary channel, a calibrated exhaust valve which is able to bring said conduit into communication with the atmosphere when the pressure in said conduit exceeds said predetermined pressure value.
Thus, by virtue of the present invention, the safety system acts at the level of the injection of the jet of respirable gas and advantageously complements the safety systems of the known devices mentioned above which safety systems act at the level of the patient""s airways.
It should be noted that in order to obtain the maximum level of safety sought by the present invention, the combination of the device for loss of head and the calibrated exhaust valve is indispensable. This is because the device for loss of head lowers the flow rate and pressure of the jet of respirable gas so that, when this pressure exceeds said predetermined value, the exhaust valve is able to evacuate the entire jet of respirable gas into the atmosphere. If said device for loss of head were to be omitted, the flow rate and the pressure of the jet of respirable gas would be able to reach values such that said jet would be able at least in part to pass through said calibrated exhaust valve in the direction of the patient""s airways, instead of being evacuated into the atmosphere. This could then result in serious injury to the patient.
Such a device for loss of head can be of any known type, such as needle screw restrictions, channels of small internal diameter, etc., and the same applies to said calibrated exhaust valve, which can be of the type with plunger and pierced cylinder, with a ball or flap charged by a spring, etc.
Said device for loss of head is preferably adjustable in such a way as to make it possible to impose on said jet of respirable gas a plurality of predetermined flow rate values and pressure values. Likewise, it is advantageous for the calibration of said exhaust valve to be adjustable. Thus, it is possible to adapt the device according to the present invention to the particular case of each patient.
Especially in the case where at least part of the conduit connecting the source of respirable gas to the auxiliary channel is incorporated in said tube, the device for loss of head and/or said calibrated exhaust valve could also be incorporated in said tube. However, they are preferably external to it.
By virtue of the device for loss of head, it is particularly easy to provide a humidifier in said conduit connecting the source of respirable gas to the auxiliary channel. This is because this device for loss of head makes it possible to lower the pressure of the jet of respirable gas to a level permitting good humidification thereof. It is thereby possible to prevent the patient""s mucous membrane from drying out. Said humidifier is preferably arranged between the device for loss of head and the calibrated exhaust valve.
Moreover, in order to prevent the jet of humidified respirable gas from directly hitting the mucous membrane, and the risk of its kinetic energy causing trauma to said mucous membrane, it is advantageous if, as is described in European Patent EP-A-0 390 684, at least the distal end of said auxiliary channel opening into the main channel is parallel to the latter and if there are provided, opposite the distal orifice of said auxiliary channel, means for deflecting said jet of respirable ventilation gas toward the inside of said main channel.
Thus, the jet of humidified respirable gas, under low pressure, passing through said auxiliary channel, is deflected toward the axis of the main channel when it penetrates into the latter. Downstream of said deflection means, that is to say inside the main channel, the pressure of said jet of respirable gas falls and the jet emerges at even lower pressure via the distal orifice of the tube. Experience has shown that downstream of the distal outlet of the tube, the pressure is low and is maintained constant throughout the respiratory space. This pressure is dependent on the flow rate of respirable gas in the auxiliary channels. Consequently, with the device for respiratory assistance according to the invention, it is possible, for example, to supply humid oxygen or a humid mixture of air and oxygen directly to the lungs, at the level of the carina, and thereby to suppress the dead space which exists in the current probes and which is about one third of the total respiratory volume of adults and about half the total respiratory volume of premature babies.
The suppression of this dead space corresponds to an increase in performance of the respiratory cycle of more than 25% in all patients and of nearly 50% in certain cases.
When the device according to the invention comprises a plurality of auxiliary channels, it is advantageous for at least some of them to be supplied jointly with respirable gas. Such joint supply of said channels can be achieved by way of a distribution ring which is coaxial with said tube. Moreover, said auxiliary channels which are not jointly supplied can be used for introducing additional gaseous products such as medicinal products.
Thus, it will be seen that the device according to the invention permits, in complete safety:
humidification of the insufflated respirable gas,
long-term intubation of the respiratory assistance device without drying,
injection of medicines or anesthetics during respiratory assistance,
dynamic measurement of pressures, since it suffices to provide auxiliary channels to which appropriate probes are associated,
establishment of a microflow of respirable gas in the auxiliary channels to prevent obstruction of said channels by mucus,
an increase in the volume exchanged, since the pressure is automatically limited and there is no risk of crushing of the pulmonary capillaries,
for the same quantity of oxygen exchanged, a decrease in the amount of oxygen in the mixture, which reduces the secondary effects of the assistance,
the possibility of using respirators which are less expensive then the current respirators.